Our co-pending U.K. patent application No. 8614527 describes a method of applying a barrier coating, of polyvinylidene chloride (PVdC) for example, to hollow plastics containers or other articles by directing a stream of the liquid coating material against the back surface of a "curtain plate" so that it spreads over the said back surface to fall as a curtain from a lower edge of the plate on to the article to be coated. This is an effective way of coating the greater part of the external surface of the article, but generally an area at the top of the article, above the uppermost level at which the curtain contacts it, remains uncoated.
There is a need for a reliable method of applying coating material in cases where, for example, the whole of the outside surface needs to be covered. Since in general coating material should not contaminate the inside of a hollow article, such a method should apply only as much coating material as is required for the area to be coated (though the amount must be sufficient), and should be able to place it accurately and in such a manner that the material not only remains where it is placed, but is not placed anywhere except where it is required.
Known coating methods such as spray coating, powder coating and flow coating, are too inaccurate for this purpose. Known printing techniques are in general not suitable because the coating materials tend to be more viscous than printing inks and are more difficult to handle. In particular it is desirable to provide as little opportunity as possible for the material to collect on any part of the apparatus and remain there for any appreciable length of time, since is will then coagulate into a solid form difficult to remove.
Known coating materials for which the present invention is suitable include water-based synthetic compounds (now commonly referred to in the trade as "latices"), or solvent-based formulations. Typical compositions of coating materials for improving barrier properties are PVdC, mentioned above and synthetic resins based on ethylene-vinyl alcohols (EVOH).